Burner control apparatus



Aug. 9, 1966 R. w. BROWN 3,265,111

BURNER CONTROL APPARATUS Filed May 28, 1965 i +32 INE L 35 34 k lo l3 I2 l4 PHOTOCELL EXPOSED TO BURNER FLAME 22 To FUEL BURNER UNIT INVENTOR. RICHARD W. BROWN ATTORNEY United States Patent 3,265,111 BURNER CONTROL APPARATUS Richard W. Brown, Excelsior, Minn, assignor to Honeywell Inc., Minneapolis, Minn, a corporation of Delaware Filed May 28, 1965, Ser. No. 459,855 5 Claims. (Cl. 158-28) My invention is concerned with an improved control apparatus and particularly with an improved burner control apparatus utilizing a circuit including means to check the circuit integrity of switch contacts which are relied upon in a component checking circuit.

As is common practice in the art of burner control apparatus, the various components utilized to provide safe operation of a fuel burner unit are checked for various conditions and the various relays and switches which are relied upon for safe operation must be checked to insure their operability.

My invention is concerned with the provision of a simple circuit having a minimum number of components to provide for checking of the circuit components.

As a feature of my invention, I provide a relay operated start interlock switch, which switch is also connected in a component checking circuit. Thus, I check the circuit integrity of this switch.

My invention utilizes a flame detector having a controlled rectifier as one element thereof. Such a rectifier is a silicon controlled rectifier, commonly known as an SCR. This silicon controlled rectifier is provided with a control electrode which is controlled by a photocell exposed to the burner flame. This photocell maybe a cadmium sulfide cell having a high dark resistance and a low light resistance when exposed to the radiation from flame. This change in the state of resistance of the photocell is utilized to render the SCR conductive. While my invention has particular utility when utilizing an SCR, it is to be understood that a relay, whose winding is controlled by the photocell and having a normally open switch which is closed upon energization of the relay, can be substituted for the SCR-photocell combination above described.

My invention will be apparent to those skilled in the art upon reference to the following specification, claims and drawing, of which The single figure is a schematic representation of the preferred embodiment of my invention.

Referring to the single figure, reference numeral designates a burner control relay having a winding 11, a normally closed switch 12, and normally open switches 13 and 14. For purposes of simplicity, switch 14 has been shown as connected to conductors which are adapted to be connected to a fuel burner unit, to energize this fuel burner unit upon closing of switch 14.

Energization of relay 10 is achieved by means of a bimetal thermostat 15 which closes a switch upon a need for operation of the fuel burner unit.

Reference numeral 16 designates time delay safety cutout means having a normally closed switch 17, a bimetal operator 18, and an associated heater 19. The construction of means 16 is conventional and a time period of energization of heater 19 is effective to cause bimetal 18 to move to the right to release switch 17 causing the switch to open. After the bimetal is cooled, a manual reset button 20 may be pushed to reset the switch to the closed position.

Proper establishment of flame at the fuel burner unit is monitored by a flame detector designated generally by means of reference numeral 21. This flame detector includes a resistive type photocell 22. This photocell has a high dark resistance and a low light resistance which it assumes when subjected to flame at the fuel burner ice unit. Photocell 22 is connected in circuit with a potentiometer 23 whose tap is connected to control electrode 24 of an SCR 25. The polarity notation associated with potentiometer 23 indicates the polarity of voltage which is applied to the electrodes of SCR 25 to render the SCR conductive upon establishment of flame at the fuel burner unit.

Other components making up the preferred embodiment of my control apparatus are diodes 26 and 27. As will be apparent, diode 26 and SCR 25 are connected to conduct current in the same direction, whereas diode 27 is connected to conduct current in a direction opposite tothat which is caused by the connection of diode 26.

Operating voltage is provided from a transformer 30 having a primary winding 31 adapted to be connected to a source of AC. voltage, and having a secondary winding 32 including end terminals 33 and 34, and a tap 35.

Considering the operation of my control apparatus, it will be assumed that thermostat 15 closes to indicate a need for operation of the fuel burner unit. The winding 11 of relay 1!) is energized from a circuit which can be traced from transformer end terminal 33 through switch 17, thermostat 15, diode 26, winding 11, heater 19, and

switch 12 to transformer end terminal 34. In order for relay winding 11 to be energized, it is necessary that switch 17 be closed and that heater 19 have electrical continuity. It is also necessary that switch 12 be closed. As will be apparent, a feature of my invention is the checking of the circuit integrity of switch 12, this switch also being in a component checking circuit, to be described.

Energization of the winding of relay 16 causes switches 13 and 14 to close. Closing of switch 1 energizes the fuel burner unit in an attempt to establish flame thereat.

Closing of switch 13 completes an intermediate energizing circuit for the winding of relay 10, which circuit can be traced from transformer end terminal 33 through switch 17, thermostat 15, diode 26, coil 11, heater 19, and switch 13 to transformer tap 35. Normally, flame is established at the fuel burner unit a short time interval after the energization of the winding of relay 10 and the resistance of photocell 22 is decreased to a point where a voltage is developed at the wiper of potentiometer 23 causing SCR 25 to become conductive.

Conduction of SCR 25 completes a holding energizing circuit for the winding of relay 10 which can be traced from transformer end terminal 33 through switch 17,

thermostat 15, diode 26, winding 11 and SCR 25 to transformer tap 35.

A further circuit which is established when SCR 25 becomes conductive places a short circuit in parallel with heater 19 and therefore operatively deenergizes this heater. This can be seen by tracing the circuit from the upper terminal of heater 19 through SCR 25 and switch 13 to the lower terminal of the heater.

If a flame failure should subsequently occur, SCR 25 is rendered nonconductive and heater 19 is operatively energized to cause a safety lockout condition after a time period of energization of this heater.

As I have mentioned, one of the features of my invention is a circuit by which I check the circuit integrity of switch 12, this switch being in the start circuit and in a component checking circuit. By a component checking circuit I mean a circuit which causes operative energization of heater 19 during the standby condition in the event that flame detector 21 fails in a manner to falsely indicate the presence of flame. The component checking circuit can be seen by tracing a circuit from transformer end terminal 34 through switch 12, heater 19, and SCR 25 to transformer tap 35. From this circuit it can be seen that if a failure should occur causing false conduction of SCR 25, when in fact a flame is not present at the fuel burner unit, then heater 19 is operatively energized and a safety lockout condition occurs such that a subsequent call for operation of the fuel burner unit, as evidenced by the closing of the switch of thermostat 15, is not effective to energize the winding of relay 10.

Other modifications of my invention will be apparent to those skilled in the art and it is intended that the scope of my invention be limited solely by the scope of the appended claims.

I claim as my invention: 1. Control apparatus for use with a fuel burner unit, comprising:

a control relay having a winding, a normally closed switch, and first and second normally open switches,

circuit means including the first normally open control relay switch adapted to be connected to the fuel burner unit,

flame detector means adapted to detect the presence of flame at the fuel burner unit and including a normally nonconductive circuit element which is conductive in response to the presence of flame,

safety cutout means including electrically energizable time delayed actuating means,

initial energizing circuit means for the winding of said control relay and including in series the winding, the actuating means of said safety cutout means, and the normally closed control relay switch,

intermediate energizing circuit means for the winding of said control relay and including in series the winding, the actuating means of said safety cutout means, and the second normally open control relay switch,

holding energizing circuit means for the winding of said control relay and including in series the winding, and the flame detecting means circuit element,

and circuit means for energizing the actuating means of said safety cutout means independent of the control relay winding and including in series the actuator, the normally closed control relay switch, and the flame detecting means circuit element.

2. Burner control apparatus for use with a fuel burner to energize the same under the control of a thermostat or the like, the apparatus comprising:

a relay adapted when energized to energize the burner unit and having a normally closed switch and a pair of normally open switches,

a safety switch having a bimetal operator and a heater,

a normally nonconductive control rectifier having means to render the same conductive upon the presence of flame at the burner unit,

circuit means controlled by the thermostat to initially energize said relay through a series circuit including said heater and said normally closed switch, to maintain the energization before flame is established at the burner unit through a series circuit including said heater and one of said normally open switches, and to maintain the energization after flame is established at the burner unit through a series circuit including said control rectifier,

and component checking circuit means to energize said heater upon a conductive failure mode of said control control rectifier through a series circuit including said normally closed switch and said control rectifier.

3. In a burner control having a control relay with a normally closed start interlock switch and a normally open switch which is adapted to be connected to the fuel burner unit, a safety switch having a time delayed actuator operative to time a trial for flame period, and an SCR having a control circuit including flame sensing means and having a current carrying circuit which is rendered conductive upon the establishment of flame, the improvement comprising:

a relay initial energizing circuit including the start interlock switch and the safety switch actuator,

a relay holding circuit including the SCR current carrying circuit,

and a component checking circuit including the SCR current carrying circuit, the start interlock switch, and the safety switch actuator.

4. Burner control apparatus having a control relay including a winding and switches, a bimetal operated safety switch including a heater, and an SCR having a control circuit including flame sensing means and having a current carrying circuit which is rendered conductive in the presence of flame, the improvement comprising:

electrical circuit means interconnecting the relay, the safety switch, and the SCR current carrying circuit; to provide a start circuit which includes the relay winding, a relay switch which is closed when the relay is deenergized, and the heater; to provide a run circuit which includes the relay winding and the SCR current carrying circuit; and to provide a component checking circuit which includes the SCR current carrying circuit, the heater, and the relay switch which is connected in the start circuit.

5. A burner control, comprising:

a transformer having end terminals and a tap,

a normally closed safety switch having a bimetal operator and a heater,

a burner relay having a winding, a closed switch and a normally open switch,

a first and a second diode,

a flame responsive SCR having a control circuit including flame sensing means and having a current carrying circuit which is rendered conductive in the presence of flame,

first circuit means extending from one of the transformer end terminals to the other transformer end terminal and including in a series circuit said safety switch, said first diode, said relay winding, said heater, and said normally closed relay switch,

second circuit means connecting said second diode in parallel with said relay winding and in a current conducting direction which is opposite to the connection of said first diode in said first circuit means,

third circuit means extending from said one of the transformer end terminals to the transformer tap and including in a series circuit said safety switch said first diode, said relay winding, and said SCR current carrying circuit, said SCR being connected in a current conducting direction which is the same as the connection of said first diode,

and fourth circuit means connected in parallel with said heater and including in a series circuit said normally open relay switch and said SCR current carrying circuit.

References Cited by the Examiner UNITED STATES PATENTS 2,695,661 11/1954 Porter 158-28 3,174,528 3/1965 Staring 158-28 JAMES W. WESTHAVER, Primary Examiner. 

1. CONTROL APPARATUS FOR USE WITH A FUEL BURNER UNIT, COMPRISING: A CONTROL RELAY HAVING A WINDING, A NORMALLY CLOSED SWITCH, AND FIRST AND SECOND NORMALLY OPEN SWITCHES, CIRCUIT MEANS INCLUDNG THE FIRST NORMALLY OPEN CONTROL RELAY SWITCH ADAPTED TO BE CONNECTED TO THE FUEL BURNER UNIT, FLAME DETECTOR MEANS ADAPTED TO DETECT THE PRESENCE OF FLAME AT THE FUEL BURNER UNIT AND INCLUDING A NORMALLY NONCONDUCTIVE CIRCUIT ELEMENT WHICH IS CONDUCTIVE IN RESPONSE TO THE PRESENCE OF FLAME, SAFETY CUTOUT MEANS INCLUDING ELECTRICALLY ENERGIZABLE TIME DELAYED ACTUATING MEANS, INITIAL ENERGIZING CIRCUIT MEANS FOR THE WINDING OF SAID CONTROL RELAY AND INCLUDING IN SERIES THE WINDING, THE ACTUATING MEANS OF SAID SAFETY CUTOUT MEANS, AND THE NORMALLY CLOSED CONTROL RELAY SWITCH, INTERMEDIATE ENERGIZING CIRCUIT MEANS FOR THE WINDING OF SAID CONTROL RELAY AND INCLUDING IN SERIES THE WINDING, THE ACTUATING MEANS OF SAID SAFETY CUTOUT MEANS, AND THE SECOND NORMALLY OPEN CONTROL RELAY SWITCH, HOLDING ENERGIZING CIRCUIT MEANS FOR THE WINDING OF SAID CONTROL RELAY AND INCLUDING IN SERIES THE WINDING, AND THE FLAME DETECTING MEANS CIRCUIT ELEMENT, AND CIRCUIT MEANS FOR ENERGIZING THE ACTUATING MEANS OF SAID SAFETY CUTOUT MEANS INDEPENDENT OF THE CONTROL RELAY WINDING AND INCLUDING IN SERIES THE ACTUATOR, THE NORMALLY CLOSED CONTROL RELAY SWITCH, AND THE FLAME DETECTING MEANS CIRCUIT ELEMENT. 